Request redirection for the MCP server mounted with FastAPI

[Archerll]

Question

While trying to use the code recommended in the README, I found that I couldn't access the /echo and /math endpoints.

Here is the environment I'm using:

• fastapi = 0.115.12
• mcp = 1.9.3

and I followed the example code exactly as provided.

# echo.py
from mcp.server.fastmcp import FastMCP

mcp = FastMCP(name="EchoServer", stateless_http=True)


@mcp.tool(description="A simple echo tool")
def echo(message: str) -> str:
    return f"Echo: {message}"

# math.py
from mcp.server.fastmcp import FastMCP

mcp = FastMCP(name="MathServer", stateless_http=True)


@mcp.tool(description="A simple add tool")
def add_two(n: int) -> int:
    return n + 2

# main.py
import contextlib
from fastapi import FastAPI
from mcp.echo import echo
from mcp.math import math


# Create a combined lifespan to manage both session managers
@contextlib.asynccontextmanager
async def lifespan(app: FastAPI):
    async with contextlib.AsyncExitStack() as stack:
        await stack.enter_async_context(echo.mcp.session_manager.run())
        await stack.enter_async_context(math.mcp.session_manager.run())
        yield


app = FastAPI(lifespan=lifespan)
app.mount("/echo", echo.mcp.streamable_http_app())
app.mount("/math", math.mcp.streamable_http_app())

After running the ​​main​​ application, when requesting:

http://localhost:8000/echo
http://localhost:8000/math

I encountered the following error:

INFO:     "POST /echo HTTP/1.1" 307 Temporary Redirect
INFO:     "POST /echo/ HTTP/1.1" 404 Not Found
INFO:     "POST /math HTTP/1.1" 307 Temporary Redirect
INFO:      "POST /math/ HTTP/1.1" 404 Not Found

I'm not sure how to resolve this issue. Perhaps this section could be explained in more detail in the README?

Additional Context

mcp = 1.9.3
python = 3.12.9

[Archerll]

I tried changing the endpoints /echo and /math to /echo/ and /math/, but it didn't work.

[author31]

i modified the mcp.streamable_http_path, and it worked. I dont know why? Hoping someone would explain it better.

echo.mcp.streamable_http_path = "/mcp/analytic"
app.mount("/", echo.mcp.streamable_http_app())